diff --git a/bld/build-namelist b/bld/build-namelist
index 8dc6c838da..af4499292b 100755
--- a/bld/build-namelist
+++ b/bld/build-namelist
@@ -2253,15 +2253,24 @@ if ($chem eq 'trop_mam_oslo' or $chem eq 'tropstrat_mam_oslo') {
     my $first = 1;
     my $pre = "";
     my $val = "";
+    my $errstr = "";
     foreach my $id (sort keys %species) {
         my $rel_filepath = get_default_value($species{$id} );
-        my $abs_filepath = set_abs_filepath($rel_filepath, $inputdata_rootdir);
-        $val .= $pre . quote_string($id . $abs_filepath);
-        if ($first) {
-            $pre = ",";
-            $first = 0;
+        if ($rel_filepath eq "") {
+            my $idstrip = $id =~ s/[ ].*//r;
+            $errstr .= $eol . "  No default filepath for $idstrip";
+        } else {
+            my $abs_filepath = set_abs_filepath($rel_filepath, $inputdata_rootdir);
+            $val .= $pre . quote_string($id . $abs_filepath);
+            if ($first) {
+                $pre = ",";
+                $first = 0;
+            }
         }
     }
+    if ($errstr ne "") {
+        die "Default emission datasets not found:" . $errstr . $eol;
+    }
     add_default($nl, 'srf_emis_specifier', 'val'=>$val);
     unless (defined $nl->get_value('srf_emis_type')) {
         add_default($nl, 'srf_emis_type',      'val'=>'CYCLICAL');
@@ -2323,7 +2332,7 @@ if ($chem eq 'trop_mam_oslo' or $chem eq 'tropstrat_mam_oslo') {
         }
     }
     if ($chem eq 'tropstrat_mam_oslo') {
-    
+
         my @files = ('soil_erod_file',
 #                    'xs_long_file', 'rsf_file', 'exo_coldens_file' );
 #                    'xs_long_file', 'xs_short_file', 'xs_coef_file', 'rsf_file', 'exo_coldens_file' );
diff --git a/bld/namelist_files/use_cases/1850_cam6_noresm_tropstratchem_aer2014.xml b/bld/namelist_files/use_cases/1850_cam6_noresm_tropstratchem_aer2014.xml
index f33815313e..bb665275c9 100644
--- a/bld/namelist_files/use_cases/1850_cam6_noresm_tropstratchem_aer2014.xml
+++ b/bld/namelist_files/use_cases/1850_cam6_noresm_tropstratchem_aer2014.xml
@@ -34,9 +34,7 @@
 <ext_frc_cycle_yr>  1850       </ext_frc_cycle_yr>
 
 <!-- surface emissions -->
-<srf_emis_specifier hgrid="0.9x1.25">
-  'SPECIES -> NOTAVAILABLE'
-</srf_emis_specifier>
+<!-- No srf_emis_specifier for hgrid="0.9x1.25" -->
 <srf_emis_specifier hgrid="1.9x2.5">
   'BC_AX  ->  $INPUTDATA_ROOT/atm/cam/chem/emis/cmip6_emissions_version20211124/perturbations/emissions_cmip6_noresm2_BC_AX_anthrosurfALL_surface_2014_date_1850_1.9x2.5_version20211124.nc',
   'BC_N   ->  $INPUTDATA_ROOT/atm/cam/chem/emis/cmip6_emissions_version20211124/perturbations/emissions_cmip6_noresm2_BC_N_anthrosurfALL_surface_2014_date_1850_1.9x2.5_version20211124.nc',
@@ -105,9 +103,7 @@
 </srf_emis_specifier>
 
 <!-- 3D emissions -->
-<ext_frc_specifier hgrid="0.9x1.25">
-  'SPECIES ->  NOTAVAILABLE'
-</ext_frc_specifier>
+<!-- No ext_frc_specifier for hgrid="0.9x1.25" -->
 <ext_frc_specifier hgrid="1.9x2.5">
   'BC_AX  ->  $INPUTDATA_ROOT/atm/cam/chem/emis/cmip6_emissions_version20211124/perturbations/emissions_cmip6_noresm2_BC_AX_airALL_vertical_2014_date_1850_1.9x2.5_version20211124.nc',
   'BC_AX  ->  $INPUTDATA_ROOT/atm/cam/chem/emis/cmip6_emissions_version20211124/perturbations/emissions_cmip6_noresm2_BC_AX_anthroprofALL_vertical_2014_date_1850_1.9x2.5_version20211124.nc',